Drug Allergies - Topic Overview
What is a drug allergy?
A drug allergy happens
when you have a harmful reaction to a medicine you use. Your body’s
immune system fights back by setting off an
allergic reaction. Most drug allergies are mild, and
the symptoms go away within a few days after you stop using the medicine. But
some drug allergies can be very serious.
Some drug allergies go
away with time. But after you have an allergic reaction to a drug, you will
probably always be allergic to that drug. You can also be allergic to other
drugs that are like it.
A drug allergy is one type of harmful, or
adverse, drug reaction. There are other kinds of adverse drug reactions. Symptoms and treatments of different kinds of adverse
reactions vary. So your doctor will want to find out if you have a true drug
allergy or if you have another type of bad reaction that isn't as
What are the symptoms?
The symptoms of a drug
allergy can range from mild to very serious. Most of the time they appear within 1 to 72 hours. They include:
- Hives or welts,
a rash or blisters. These are the most common symptoms of drug
allergies. See a picture of
skin reactions caused by drug allergies .
- Coughing, wheezing, a
runny nose, and trouble breathing.
- A fever.
- A serious
skin condition that makes your skin blister and peel. This problem is called
toxic epidermal necrolysis, and it can be deadly if it
is not treated.
- Anaphylaxis, which is the most
dangerous reaction. It can be deadly, and you will need emergency treatment.
Symptoms, such as hives and trouble breathing, usually appear within 1 hour
after you take the medicine. Without emergency care, you could die.
What medicines commonly cause an allergic reaction?
Any medicine can cause an allergic reaction. A few of the most common
- Penicillins (such as ampicillin or amoxicillin).
If you are allergic to one medicine, you may be allergic
to others like it. For example, if you are allergic to penicillin, there is a chance that you may also
be allergic to similar medicines, such as amoxicillin.
How is a drug allergy diagnosed?
Your doctor will
diagnose a drug allergy by asking you questions about the medicines you take
and about any medicines you have taken in the recent past. Your doctor will
also ask about your past health and your symptoms. He or she will do a physical
If this doesn't tell your doctor whether you have a drug
allergy, then he or she may do skin tests. Or your doctor may have you take
small doses of a medicine to see if you have a reaction.